Method of and apparatus for the reproduction of sound



June 17, 1941. J. E. DICKERT 2,245,652

METHOD OF AND APPARATUS FOR THE REPRODUCTION OF SOUND Filed Dec. 7, 1938 I 4?" FILTEB 05C! LLATOB .58 41 z 5W Q5551; 1 42 16 15 AMPLIFIER 5 I CARRIE l 27 m; 45

i2 F -r RgCTIFIEB u. are 9vv0- F7562 AMI? 0/3 SPEAKEB 2530 P0 rsmw. amt/m Patented June 17, 1941 METHOD OF AND APPARATUS FOR THE REPRODUCTION OF SOUND James E. Dickert, Highland Park, Ill., assignor to World Broadcasting System, Inc., New York, N. Y., a corporation of Delaware Application Dccember'l, 1938, Serial No. 244,436

31 Claims.

The invention relates generally to the audible reproduction of message matter or sound such as instrumental or vocal music, talking, or combinations thereof, and more particularly it relates to those systems of audible production and reproduction of message matter of this character which involve the transmission of energy representing a function of the original sound-intensity through an intermediate or transmission media, such as wire lines, a radio carrier, and/or recording means, to areproducer for audible reproduction.

The primary purpose and objective of the present invention is to enable sound sequences or programs of all types to be reproduced with a dynamic range of the original source despite the restrictions of present-day transmission media.

In the production of audible message matter or programs of this character, as for example, in a radio program, there may be, within the audible range, a variation of as much as 60 decibels between the loudest and softest sound, and, since such variations represent major elements of the artistry put into the production of the program, it is usually desirable that these expressions be preserved or easily controlled so that the envelope of intensity curve or dynamic pattern of the original may be attained in the reproduction.

There are, however, certain mechanical and physical limitations inherent in the particular intermediate media commonly employed, so that it has been necessary for the various industries to adopt make-shift expedients which cause marked and objectionable distortion and dynamic alteration of the reproduced sound. The limitations of the commonly used intermediate media are such that before the varying power impulses or energy created or induced by the audibly produced sound are impressed upon or transmitted to the intermediate media, these impulses must be reduced in intensity at their strongest portions so as not to exceed the permissible maximum capabilities for the particular intermediate media.

While it may be suggested that this undesired modification of the intensity of the sound sequence might be avoided by uniformly (rather than variably) reducing the intensity of the sound-induced impulses, such an expedient cannot be used in practice, since it would decrease the signal-to-noise ratio to such an extent as to render the less intense portions of the desired program unintelligible. This troublesome situation arises from the fact that, in the various commonly used intermediate media, there is a substantially fixed noise background which must be exceeded by the signal intensity at all times in order to insure intelligibility of the desired impulse or signal. In telephone transmission such noise background is known as line noise; in radio or carrier wave transmission it comprises various types of static as well as noises inherent in the transmitter and receiver; while in recorded programs it is caused by noises mechanically introduced in the recording and the pickup from the record and is commonly known as surface noise.

Hence the sound engineer must not only reduce the transmitted intensity of the louder portions of the program, but must also increase the transmitted intensity of the softer portions so as. to exceed the fixed noise level of the intermediate media. This operational practice, including both increase and decrease of the amplification, is known to members of the profession simply as squeezing. This necessary variation or squeezing reduces the fidelity of reproduction.

Thus it is found that where the original sound is picked up by a microphone and transmitted electrically by an intermediate media such as a wire line or radio carrier wave, the portions of highest intensity must. be reduced, and the portions of lowest intensity must be increased, so that the ratio of maximum to minimum in the energy transmitted to the intermediate media does not exceed 30 decibels. Similarly, when the intermediate media includes the step of recording, the maximum variation of the energy applicable thereto is limited to from 20 to 30 decibels as determined by the method or type of recording employed.

In practice it is found that a large percentage of the programs, selections, or messages which are to be transmitted or recorded for reproduction purposes involve variations in sound-intencity which exceed the capacity or limitations of the intermediate media to be employed. As a result, the sound engineer supervising the recording or transmission of a particular selection or program appropriately reduces the amplification in the sound pick-up system when largevolume portions of the program are being produced. Having thus varied the transmitted sound-intensity to meet the maximum physical limitations of the equipment employed, the engineer has transmitted to the intermediate media a program which does not faithfully'represent the original. Hence, the original program or selection, with the contrast, expression and forcefulness which has been so earnestly sought in its The resulting dynamic distortion of the reproduced' sound sequence has long been recognized as being highly objectionable,'and various expedlents looking toward reestablishment of the original intensity curve have been widely used and commercially exploited. Such-an effort to obtain the desired fidelity of reproduction involved the use of devices known commercially as expanders, such devices having been. incorporated in amplifiers associated with radio receivers, telephone circuits, and in phonographs of various kinds. Such expander devices operated upon the assumed principle that extremely high volume portions of a transmitted sound sequence had originally been suppressed or lowered in intensity, andshould, therefore, be expandedor made louder by the reproducer,'while portions of low intensity should be made of less intensity upon the assumption that they had been amplified at the outset toover-ride background noise.

. Such expanders were operative in accordance .sound sequence, program or musical selection,

but also with the individual preferences of the particular sound engineer, it will be evident that such automatically produced corrective measures could rarely, if ever, result in a truly faithful reproduction. Furthermore, such. expanders involve a time-delay action which, in the reproduction of many types of program, produce incongruous results which are apparent even to the most inexpert audience.

In view of the foregoing, a morespeciflc oblect of the present invention is to provide a new and improved sound system or method and. apparatus whereinthe corrective changes in amplification initially applied to the sound sequence are automatically and accurately applied in an inverse ratio to the reproducing means so as to cause more faithful reproduction of the original sound sequence.

Another object is to provide a method of sound transmission and reproduction whereby the exa,a4s,esa I v immaterial, whereby to save the expense and deerfidelity and intelligibility of reproduction. In

lay and improper results which would arise un- "der present-day practice.

program-whereby to completely obliterate the objectionable noise background and insure great the application of this phase of the invention to the recording art, there is amarked increase in the useful life 'of the records, since the usual increase of surface noise with the age of the rec- 0rd becomes immaterial.

Another object is to provide an improved system or method of wire line transmission wherein line noise becomes less important and less trou-. blesome than in prior systems.

A further object is to provide a novel sound system or method adapted for use in carrier wave transmission and capable of more accurately reproducing the original program so far as the variations of sound-intensity are concerned.

Another object is to produce a new and improved method of recording sound.

Another object is to produce a new and improved sound record.

Another obiect is to produce a new and improved radio receiver.

pansion or reduction of intensity of all or any a portion of the reproduced sound may be readily and accurately controlled by the sound engineer to obtain the desired dynamic pattern in such reproduction.

A further and more specific object is to produce a new and improved sound system or method and apparatus which lends itself to ready manipulation to accentuate, vary or emphasize particular sounds of portions of the program which are not capable of proper production in the studio, as for example, a shot or explosion.

Another object is to provide a' new and improved sound system or method of sound reproduction wherein there is available at the reproducer for accurate and faithfully patterned reproduction the full range of intenslty variation of decibels. v

A further object is to provide a sound system or method of this character wherein mistakes or slight delays of the sound engineer in "squeez- Another. object is to produce a new andimproved phonographic reproducer.

Another object is toproduce new and improved apparatus for the reproduction of sound in con; nectionwith the projection of sound motion pictures.

A general object of the invention is to provide apparatus for carrying outthe various methods or systems hereinabove specified.

Other objects and advantages will become apparent from the following description, taken in connection with the accompanying drawing, in which Fig. 1 is a block diagram illustrating a pre- Fig. 3a is a fragmental illustration of a por tion of a reproducer circuit, based on the circuit of Fig. 2, but modified for use in connection with the apparatus of Fig. 3.

- In, accordance with the present invention, the limitations of the intermediate or transmission media so far as permissible intensity-variations are concerned are rendered immaterial, and the desired correspondence between the dynamic patterns of an original sound sequence and a reproduction thereof is obtained through the use of a variable dynamic control signal, which control signal is preferably created and varied as an incident to and in accordance with the requi ed squeezing of'the transduced sound sequence, and

is automatically utilized as an incident to the reproduction process to reverse-the originally applied squeezlng proces and thereby restore the ori inal dynamic oattem of the sound-sequence.

In Fig. 1 of the drawing an apparatus for carrying out this novel method is illustrated diagrammatically by means of a block diagram, the

various elements of the system being identified thereon in a generic sense because of the wide range of usefulness of the system. Thus the system includes a transducer such as a 'microphone ll connected by a on path It to' an amplifier l2ywhereby electrical vibratiom induced by the desired sound sequence are amplified for transmission over a path it to an intermediate transmission media l4. diate media may be any one of the several known f types, such as recording and re-pickup, carrier mis'sible intensity-variation inherent in the various types of intermediate media i4,- it is often impossible toattain true dynamic correspondence between the original and reproduced sound sequence. This objectionable limitation of con- This interme ,acaesa I nod or squeezed to make it conform with the limitations of the intermediate media, and the second of which constitutes a distinguishable control signal timed in relation to the audio signal and indicative of the varying corrective amplification which must be applied to the squeezed audio signal in its reproduction in order elements thus far specifically -enumerated, but by reason of the limitations as to maximum perventional sound systems is overcome by the presproduction process to restore the original dynamic pattern of the sound sequence.

This end is attained through .the use of a control signal having characteristics distinguishable from those portions of the sound sequence which are to be audibly reproduce d. Present-day standards provide that reproducers which will reproduce frequencies up to 8000 cyclesper second are to be termed high fidelity reproducers, and upon this ba sis,any frequency beyond 8000 cycles may be used as a control signal. Hence, for purposes of illustration, I have chosen 9000 cycles as the control frequency to be employed, and have inserted in the transmission path i I adjacent the microphone iii a filter 20 whereby all sound-induced frequencies above 8000 cycles are filtered from the circuit. i

The desired control signal is, in the system herein shown, generated by an oscillator 2| set for the generation of 9000 cycle current, which is fed through a filter 22 sharply tuned to pass only 9000 cycle current to an attenuator 23 which limits the voltage to be transmitted. This uniform 9000 cycle control signal is passed through a variable resistance 24 to the transmission path II which resistance 24 is arranged in parallel with a volume control 25' in the path ll. Separate volume controls 24 and 25 are used in the present instance, but the same control. could .be used by correspondingly altering certain features of the reproducer as will be hereinafter explained. The two control elements 24 and 25 are, however, operated in unison by a common volume control element 26 which is so connected that when the intensity of the transduced sound energy is reduced, the transmitted intensity of the control signal is increased in a predetermined ratio. Similarly, when the intensity of the transmitted sound energy is increased, as when it is desired to increase the signal-to-noise ratio, the transmitted intensity of the control signal is reduced in accordance with the predetermined ratio.

Hence, two related signals are produced. one of which constitutes a desired audio signal, modito restore the original dynamic or amplitude pattern. While individual transmission of these two related 'signals'is possible, ,I prefer tocombine the two or to form a composite signal which is amplified and transmitted to the intermediate media. I After the composite signal has been transmitted through the intermediate media l4, the two distinguishable elements or signals are separated so that the audio signal may be used to reproduce the desired sound while the control signal may be employed to govern the dynamic or amplitude pattern of such reproduced sound. This end is attained in the present illustrative embodiment by feeding the composite signal from the intermediate media i4 along two parallel paths 21 and 28, one path 21 of which embodies a filter 30 which passes the desired audio signal only, that is, the frequencies from, say 30 cycles, to 8000 cycles, while the other path 28 includes a filter 3| which passes only the control signal of 9000 cycles. The separate signals are then applied to the amplifier It, the desired audio signal being applied so as to amplify the transduced sound energy while the control signal is passed through a rectifier and filter 33 and the resulting direct current is then applied so as to vary the amplification or modify the volume of the transduced sound energy in an opposite ratio to the originally applied squeezing. Hence the transduced'sound energy acts upon the speaker iii to reproduce the sound sequence in a dynamic or amplitude pattern corresponding with the original.

While the system has been-herein described as attaining exact correspondence between the dynamic patterns of the original and reproduced sound sequence. it is to be understood that such exact correspondence is not desired in every instance, and that the system of the present invention is highly flexible in enabling the sound engineer to obtain practically any desired dynamic pattern in the reproducion. Thus,the present invention may be employed to expand or reduce all or any desired portion of a sound sequence, and such variation may be in any desired ratio within practical limits. This end may be attained in a variety of ways, as for example, by insertion of a variable resistance in the control signal path between the control 24 and the path ll or by adjustment of the attenuator 23; or by varying the type or characteristics .of the control 24; or the reproducer may be designed to give a similar controlling action by inserting a variable resistor between the rectifier 33 and the amplifier l6.

When the intermediate media includes the step of recording, the composite signal passes from the amplifier l2, and by means of the properly other forms of recording means; and upon the taught by the present disclosure, the illustration and description will herein be confined to phonographic recording upon a disk record II supported by a conventional turntable a (Fig.

8). Hence, with the arrangement, the com-- posite si al is impressed upon the record ll.

when thismecord is placed upon turntable 40 (Fig. 2) of a phonographic reproducer, this composite signal is picked up by the electrical pickup ll and transmitted along the path 42 through the .properly set switch ll, to the reproducing apparatus. One form or embodiment of apparatus suitable for reproducing the composite signal thus formed with the apparatus of Fig. l is shown in detail in Fig. 2, this particular reproducer being shown as deriving its signal from the electrical phonographic pickup H, but being capable of operative association with any of the various types 01 intermediate media.

In the reproducer'oi' Fig. 2 the composite signal'energy derived from the intermediate media" is transmitted through a transformer coupling 44. and from the high side of the transformer secondary iafed along the two parallel paths 2! and 28, wherein the desired audio signal and the control signal are separated as explained in connection with Fig. i. The filter 30 shown in the path 21 in Fig, 2 is constructed-and connected in accordance with known principles to attenuate the 9000 cycle control signal and to pass the audio frequencies which are to be reproduced, such for example as those frequencies between 30 cycles and 8000 cycles, and this audio signal is impressed through a wire 45 upon the normal control element or amplifier grid 48 of a thermionic amplifier tube 41. The tube ll constitutes one or many possible embodiments of the amplifier I! described in connection with Fig. 1, and in the present instance I have illustrated this tube as being of the commercially known 6L7 type. This tube serves as a volume modifying means, and it will be understood that the same ultimate end might be attained by many types of apparatus, such for example, as a thermionic pad whereby the sound-intensity is variably attenuated after a relatively large and uniform initial amplification, rather than variably amplified in the strict sense. The plate circuit of the amplifier 41 is conventionally connected to leads 4! which may be connected to a further stage of amplification, or to a reproducer such as thespeaker I! of Fig. l.

The other path 28 has a sharply tuned filter Ii associated therewith as shown in Fig. 2, so that the frequencies otherthan the 9000 cycles control signal 'are filtered ofi to ground and the control signal is passed along a conductor 28' to the amplifier grid 50 of a thermionic amplifier 5|. This control signal a mplifier 5i may be formed by a conventional 6E6 tube, and its plate 52 is transformer coupled at 51 to the control frequency rectifier and filter 33. The rectifier tube is herein shown as being of the conventional 6H6 type and is indicated by the numeral 54. The connections of the two diodes of the tube II are such as to provide a full wave rectifier, and there is included a filtergor condenser 55, whereby the output of the rectifier is a continuous direct current the varying intensity of which represents a function of the varying intensity of the originally transmitted control signal.

The output circuit of the control signal filter and rectifier it includes a load resistor 56, and the necessary portion of the rectified filtered voltage is taken from this load resistor 58 and is impressed through a conductor 51 upon the indecticn element or grid ll of the audio-signal amplifier l'l. when'the control signal has been formed by the system illustrated in Fig. 1, the load resistor I. is located in the positive portion of the circuit, that'is, in the cathode lead. Thus when an increase of intensity of the rectified and filtered control signal indicates that an increased amplification of the audio signal is required, this increased positive voltage is-applied to the conductor 51 and acts to bring about the necessary increase of amplification in the tube 41. This tube 41. as herein shown, exhibits its greatest amplification when the injection grid 00 is least negative, and its amplification decreases as the negative potential on the injection grid is increased. Hence the lower side of the load resistor It is connected, as indicated at It, to a source of relatively high negative voltage, say, minus 40 volts: and as a result the injection grid 68 is normally biased negatively to such an extent as to render the tube ll insensitive. This normally blocked condition of the tube It is variably oifset by the positive portion of the rectified and filtered control signal applied through the conductor 51, so as to transmit the audio signal with the. desired or restored dynamic pattern. The absence of a control signal results, of course, in the blocking of the tube 41, and hence there can be no audible reproduction of background noise at such times.

In Figs. 8 and 3a. of the drawingI have illustrated alternative forms of apparatus embodying the invention, and with these alternative forms the variation of the control signal is in -an inverse ratio to the variation employed in the structure of Figs. 1 and 2. Thus in the system shown in Fig. 3, the transduced sound energy passes along the path li,.through the filter 20, volume control 2!, and amplifier I! to th e intermediate media, such as the'recording means 31, all constructed and related in the same manner'as in Fig. l. The control frequency is generated by a similar oscillator 2i and passes through the filter 22 and attenuator N. In the system of Fig. 3, however, the same volume control 25 is used for varying both the audio signal and the control signal, and hence the control frequency is conducted, along a path 23' from the attenuator 23 to a point between the filter 20 and the volume control II.

This reversal of the control signal variations requires correspondingly different application or the control signal to the inJection grid II. This end may be attained by modification or the rectifier circuit oi. the structure shown in Fig. 2, such a modification being shown in detail in Fig. 3a of the drawing. Thus the rectifier tube 54 is connected as a full wave rectifier with the condenser II and the load resistor 50' connected in the negative portion of the circuit, or in the plate lead. As a result, a negative potential is impressed on the injection grid BI and the intensity of this negative potential is a fimction-oi' the intensity of the control signal. Since the load resistor Iii is grounded at II, the injector grid 58 has zero potential when there is no control signal present; and it is by the increasing application of negative bias on the grid II that the amplification oi the tube 41 is reduced. Hence,

the intermediate transmission media includes various common types of recording, but it will be evident that the present invention is, likewise applicable to the other types of intermediate media II as indicated diagrammatically in Fig. l of the drawing. Thus, it will be evident that through appropriate adjustment of the switches 35 and 43 of Fig. l, the sound would be transmitted by carrier wave as indicated at 6|, or by wire lines as indicated at 62.

In constructing the present apparatus the nor-. mal intensity level of the control frequency is so adjusted that in normal variation in accordance with the squeezing applied to the audio signal, the range of intensity variation in the control signal will be within the capabilities of the intermediate media. In the reproducer, the adjustment of the intensity of the rectified control voltage applied to the injection grid 58 is attained through variation of the point of connection of the conductor 51 with the load resistor 56, or by other conventional expedients such as the variation of the normal bias applied at 60, or by variation of the amplification in the control signal amplifier In any event, the adjustment of the control impulse is such that the reproduction of any particular portion of a sound sequence is of an intensity equalling or bearing the desired intensity relation to the corresponding portion of the original sound sequence.

From the foregoing description it will be apparent that the present invention provides a method of and apparatus'for sound transmission and reproduction whereby inherent limitations in the transmission capabilities of various types of intermediatetransmission media such as carrier wave, wire lines or recording systems, are rendered immaterial, thereby to endow the reproduced sound sequences with accurately patterned and controlled dynamic characteristics heretofore unattainable.

It will also be evident that the present invention provides a new and improved sound record having greatly improved reproduction characteristics as well as an increased useful life.

In addition,.the present invention provides new and improved methods of and apparatus for sound transmission and reproduction by carrier wave as well as wire line transmission, and in each instance the invention obviates many objectionable features of prior facilities.

I claim as my invention:

1. The method of obtaining correspondence between the dynamic patterns of an audibly produced sound sequence and an audible reproduction of such sequence reproduced after transmission of a transduced representation of the sequence through an intermediate media requiring squeezing of the sound-induced representations to bring'such representations within the intensity-variation capabilities of the media, which consists in transmitting in timed relation to such representations a corrective signal which, as an representations, has been varied in intensity in predetermined ratio to such squeezing so as to be indicative of the expansion or reduction required in the intensity of the transmitted representations to restore the original dynamic pattern thereof, and automatically utilizing the corrective signal to expand or reduce such representations as an incident to the audible reproduction of the sound sequence.

2. The method of obtaining correspondence between the dynamic patterns of an audibly proincident to the squeezing of the sound induced nal which, as an incident to the squeezing of the sound induced representations, has been varied in intensity in predetermined ratio to such squeezing so as to be indicative of the expansion or reduction required in the intensity of the transmitted representations to restore the original dynamic pattern thereof.

3. The method of transmitting sound from a sound pickup system to an intermediate media having limited capacity as to intensity-variations which consists in squeezing the sound-induced energy in the sound pickup system to meet the capacity of the intermediate media, simul-- taneously varying the intensity of a continuous control signal to vary the intensity of the control signal in accordance with and in predetermined relation to such squeezing, and transmitting said squeezed sound energy and said continuous control signal to the intermediate media in predetermined timed relation to each other.

4. The method of transmitting through an intermediate media having a limited capacity as to intensity-variations a program squeezed to meet such limitations which consists in simultaneously transmitting through the same media a con-.

tinuous control impulse varying in intensity in accordance with and in predetermined ratio to the squeezing applied to the transmitted pro gram. 5. The method of transducing and transmitting through an intermediate media a sound sequence involving sound-intensity variations exceeding the limits permissible in said intermediate media which consists in reducing and varying. the intensity of the more intense portions of the sound-induced impulses transmitted to the intermediate media as required to bring such portions within the transmitting capacity of said media and simultaneously transmitting a continuous distinguishable control impulse which has been varied in intensity in predetermined ratio to such reduction and variation as an incident to such reduction and variation.

6. The method of avoiding unintelligibility in transmitted and reproduced sound due to background noise in the intermediate media which consists in applying a squeezing operation to vary the amplification of the sound-induced energy at the transmitting means to transmit such energy at the maximum signal-to-noise ratio obtainable with the particular intermediate media, and inversely and automatically varying the ultimate amplification at the receiving and reproducing means to restore the original intensity curve to the reproduced sound.

7-. The method of sound transmission through an intermediate media having limited transmission capabilities in respect to the range of permissible intensity-variation which consists in varying the amplification at the point of sound pickup so as to maintain the intensity of the transmitted sound-induced energy at substantially the maximum permissible intensity at all times and transmitting simultaneously a continuous control impulse of a distinguishable frequency and varying in intensity in accordance sound-induced energy.

8. In a sound reproducing mechanism, the. combination of a sound record having a sound track bearing a composite representation of a desired sound sequence within a predetermined range of frequencies to be reproduced and a conwith the variations in the amplification of the trol signal of a distinguishable frequency, means sensitive to said composite representation to produce electrical vibrations corresponding therewith, means for separating. the electrical vibrations representing said control signal from the range of frequencies transmitted thereby, a

volume control governing the transduced output of said pickup means, and means for introducing.

electrical vibrations representing said desired 14. The method "of producing a sound record which consists increating electrical vibrations corresponding to the sound to be recorded, creating a continuous series of electrical vibrations of uniform intensity and .of a'frequency outside the range of frequencies of the sound-induced vibrations, correspondingly reducing the intensity ofall of such'yibrations as required to bring theintensity-variation of the sound-induced'vibrations within the recording limits of the recording medium being used, and applying such soundinduced vibrations and the other vibrations to the recording medium in a predetermined relation to each other.

15. The method of producing a sound record of a sound sequence involving intensity-variations requiring squeezing of the sound-induced energy before application thereof to the recording medium which consists in applying to the recording medium in timed relation to the record of the sound-induced energy a continuous control impulse which, as an incident to the squeezing of the sound induced representations, has been varied in intensity in predetermined ratio to such into the output of said pickup system a signal of a frequency outside of said range and varying in intensity under the governing action of said volume control. g

10. In a sound system, the combination of an electrical sound pickup means'having. a transmission line connected thereto, filter means in said line for limiting the range of frequencies transmitted thereby, a frequency generator operable to produce a frequency outside of said range and connected to said line beyond said filter means, and a volume control operatively associated with said line beyond the point of connection of said frequency generator. i

11. In a sound system the combination of a transducer and an intermediate transmission squeezing so' as to be indicative of the expansion or reduction required in the reproduction process to attain the desired dynamic pattern in such reproduction of the sound sequence.

' 16. The method of producing a sound record which consists in variably reducing the stronger portions of a desired sound sequence before they are applied to the recording medium and simulmedia to receive and transmit the transduced sound, a frequency generator operable to supply a control current of predetermined frequency,

and circuit means operatively connecting said transducer and said frequency generator to said intermediate transmission media and including volume control means operable by a single control element to vary simultaneously and in predetermined relation the intensity of the transduced sound and the control current.

12. The method of producing a sound record which consists in combining sound-induced vibrations within a predetermined frequency range to be reproduced with a constant intensity signal of a frequency outside said range to form a composite signal, variably modifying the intensity of the composite signal to maintain the same within the limits of intensity-variation allowable with the particular recording medium, and applying the modified composite signal to the recording medium. I

13. The method of producing a sound record which consists in creating electrical vibrations corresponding to the sound to be recorded, creating a continuous series of electrical vibrations of uniform intensity and of a frequency outside the range of frequencies of the sound-induced vibrations, correspondingly reducing the intensity of all of such vibrations as required to bring the intensity-variation of the sound-induced vibrations within the recording limits of the recording medium being used, and simultaneously taneously applying to the recording medium a continuous control signal of distinguishable frequency and varying in intensity in a predetermined ratio to the variable reduction of the intensity of the sound sequence.

17. The method of producing a sound record to avoid the usual surface noise which consists in varying the amplification of the sound-induced energy before it is applied to the record so as to maintain a favorable signai-to-noise ratio at all times, and simultaneously applying to the record a continuous control impulse of distinguishable frequency and varying inintensity in accordance with the variations in the amplification of the sound-induced energy.

18. In a process of recording-an audibly produced sound sequence and then audibly reproducing the same, the method of obtaining correspondence between the dynamic patterns of the audibly produced and the audibly reproduced sound sequence which consists in squeezing the sound sequence to bring it within the permissible range of intensity variation and simultaneously recording in timed relation to the recording of the squeezed sound-induced energy a corrective signal which, as an incident to the squeezing of the sound sequence, has been varied in intensity in predetermined ratio to such squeezing so as to be indicative of the expansion or reduction required in the recorded indications of the sound-induced energy to restore the original dynamic pattern thereof, and automatically utilizing the corrective signal to expand'or reduce the volume of the reproduced sound sequence as an incident to the reproduction thereof.

19. A sound record having sound track means thereon representing in fixed timed relation a desired sound sequence which is to be audibly reproduced and which has been squeezed to meet the limitations of the record insofar as intensity variations are concerned and representing a continuous. control impulse which has been varied in its intensity in accordance with and as an incident to thesqueezing of the desired sound sequence and which isapplicable as an intensitycorrection to the, audibly reproduced desired sound sequence in the audible reproduction thereof.

20. A sound record having sound track means thereon representing vibrations induced by a desiredisouiid sequence and which has been varied as to amplitude so as to maintain a favorable 21. The method of carrier wave communication which consists in variably reducing the stronger portions of a desired sound sequence before they are impressed upon the transmitted carrier wave and simultaneously impressing upon the carrier wave a continuous control signal of distinguishable frequency and varying in intensity in predetermined ratio to said variable reduction of the intensity of the sound sequence.

22. The method of carrier wave transmission of sound-induced electrical vibrations lying within a given range of frequencies to be audibly reproduced which includes the application of such vibrations and also electrical vibrations of a distinguishable frequency to the carrier wave while simultaneously varying the intensity of all of said vibrations to meet transmission limitations as to dynamic range.

23. lhe method of carrier wave communication which consists in forming a composite signal consisting of a desired signal and a control signal of distinguishable frequencies varying the intensity of the composite signal as required to bring the intensity-variation of the composite signal within the maximum capabilities of the carrier, and impressing the resulting composite signal on the carrier wave to modulate the same.

24. The method of carrier wave communication which includes the steps of forming a composite signal consisting of a desired signal and control signal of distinguishable frequencies,

' varying the intensity of the composite signal so as to bring the composite signal within the range of permissible intensity-variation for the carrier, impressing the resulting composite signal on the carrier wave to modulate the same, receiving said carrier wave, separating the desired signal and the control signal, applying the desired signal to an amplifier and thence to a reproducer, and applying the control signal to the amplifier to produce in the reproduced signal an intensitycurve corresponding to a predetermined function of the intensity-curve of the original desired signal.

25. The method of wire line transmission which consists in transmitting in timed relation to the desired audio signal which has been squeezed to meet wire line transmission limitations, a variable control signal which, as an incident to the squeezing of the desired signal, has been varied in intensity in predetermined ratio to the squeezing so that the intensity of said control signal is indicative of a volume correction to be applied to such audio signal to restore the original intensity-curve of the audio signal, and automatically correcting the volume of the audio signal in its reproduction in accordance with the variations in said control signal.

26. In a sound reproducing mechanism, the combination of a sound record having a sound track bearing, in predetermined positional relationship, representations of a desired sound sequence within a predetermined range of frequencies to be reproduced and which has been varied in intensity with respect to the original audibly produced sound sequence to meet'the limitations of the record, and a control signal of a distinguishable frequency wherein said control signal has been varied in predetermined ratio to said variations in the intensity of thedesired sound sequence, means sensitive to said representations to produce electrical vibrations corresponding therewith, and amplifying and reproducing means operated by the electrical vibrations representing said sound sequence to reproduce said sound sequence, and means forming part of said amplifying and reproducing means and controlled by said control signal to govern the intensity of the reproduced sound sequence.

27. The method of carrier wave communication which consists in impressing upon the carrier wave, in timed relation to the impression of a desired signal which has been squeezed to meet the permissible intensity-variation limitations of the carrier wave, a variable control signal which, as an incident to the squeezing of the desired signal, has been varied in intensity in a predetermined ratio to the squeezing of the desired signal so that the intensity of said control signal is indicative of a volume correction to be applied to such desired signal to restore the original intensity curve of the desired signal.

28. The method of carrier wave communication which consists in impressing upon the carrier wave. in timed relation to the impression of a desired signal which has been squeezed to meet the permissible intensity-variation limitations of the carrier wave, a variable control signal which, as an incident to the squeezing of the desired signal, has been varied in intensity in predetermined ratio to such a squeezing so as to be indicative of a volume correction to be applied to such desired signal to restore the original intensity curve of the desired signal, and automatically correcting the Volume of the desired signal in its reproduction in accordance with the variations in said control signal.

29. In a sound reproducing mechanism, the combination of a sound record having a sound track bearing representations of a desired sound sequence within a predetermined range of frequencies to be reproduced and which has been squeezed so as to vary its intensity with respect to the original audibly produced sound sequence to meet the limitations of the record, and also having on said sound track, in a predetermined positional relation to said representations of said desired SOlJIld sequence, additional representations of a control signal of a predetermined distinguishable frequency wherein said control signal has been varied in intensity in predetermined ratio to said variations in the intensity of the desired sound sequence, means sensitive to said representations to produce electrical vibrations corresponding therewith, a first amplifier and an associated reproducing means operated by said electrical vibrations representing said sound sequence to reproduce said sound sequence, and control means comprising a second amplifier, a circuit to said second amplifier ineluding filter means operable to pass the electrical vibrations corresponding to said control signal from said sensitive means to said second amplifier, a full-wave rectifier operatively cou-' pled to said second amplifier, and means for applying the full wave rectified output or said full-wave rectifier to said first amplifier to restore the original dynamic pattern to the reproduction of the desired sound sequence.

30. In a' sound reproducing mechanism adapted for use with a sound record having a sound track rectified output or said mil-wave rectifier to said first amplifier to restore the original dynamic pattern to the reproduction or the desired sound I sequence.

bearing representations of a desired sound sequence within a predetermined range of frequencies to be reproduced and which has been squeezed so as to vary its intensity with respect to the original audibly produced sound sequence to meet the limitations of the record, and also having on said sound track, in a predetermined positional relation to said representations of said desired sound sequence, additional representa tions of a control signal of a predetermined distinguisha-ble frequency wherein said control signal has been varied in intensity in predetermined ratio to said variations in the intensity of the desired sound sequence, said sound reproduc- 'ing mechanism comprising means sensitive to said representations to produce electrical vibrations corresponding therewith, a first amplifier and an associated reproducing means operated by said electrical vibrations representing said sound sequence to reproduce said sound. sequence, and control means comprising .asecond amplifier, a circuit to said second amplifier including filter means operable to pass'the electrical vibrations corresponding to said control signal from said sensitive means to said second amplifier, a fullwave rectifier operatively coupled to said second,

amplifier, and means for applying the full-wave 31. In a sound reproducing mechanism adapted for use with'a sound record having a sound track bearing representations of a desired sound sequence within a predetermined range oi frequencies to be reproduced and which has been squeezed so as to vary its intensity with respect to the original audibly produced sound sequence to meet the limitations oi the record, and also having on said sound track, in a predetermined positional relation to said representations of said desired sound sequence, additional representations or a control signal 01' a predetermined distinguishable frequency wherein said control signal has been varied in intensity in predetermined ratio to said variations in the intensity or the desired sound sequence, said sound reproducing mechanism comprising means sensitive to said representations to produce electrical vibrations corresponding therewith, a first amplifier and an associated'reproducing means operated by said electrical vibrations representing said sound sethe reproduction of the desired sound sequence.

J AMES E. DICKERT. 

